The present invention relates to an improved valve gear train for an internal combustion engine, and more particularly, to a valve deactivator sub-assembly for use therein.
Although the valve deactivator sub-assembly of the present invention may be utilized to introduce some additional lash into the valve train, such that the valves open and close by an amount less than the normal opening and closing, the invention is especially suited for introducing into the valve train sufficient lash (also referred to hereinafter as xe2x80x9clost motionxe2x80x9d), such that the valves no longer open and close at all, and the invention will be described in connection therewith.
Valve deactivators of the general type to which the invention relates are known, especially in connection with internal combustion engines having a push rod type valve gear train in which there is a rocker arm, with one end of the rocker arm engaging the push rod, and the other end engaging the engine poppet valve. Typically, a central portion of the rocker arm is fixed relative to the cylinder head (or other suitable structure) by a fulcrum arrangement as is well know to those skilled in the art, in which the fulcrum normally prevents movement of the central portion of the rocker arm in an xe2x80x9cup and downxe2x80x9d direction. At the same time, the fulcrum permits the rocker arm to engage in cyclical, pivotal movement, in response to the cyclical motion of the push rod, which results from the engagement of the push rod with the lobes of the rotating cam shaft.
There are a number of known valve deactivator sub-assemblies which are operably associated with the fulcrum portion of the rocker arm and which, in the latched condition, restrain the fulcrum portion of the rocker arm to move in its normal cyclical, pivotal movement. However, In an unlatched condition, the valve deactivator sub-assembly permits the fulcrum portion of the rocker arm to engage in xe2x80x9clost motionxe2x80x9d such that the cyclical, pivotal movement of the push rod causes the rocker arm to undergo cyclical, pivotal movement about the end which is in engagement with the engine poppet valve. In other words, the rocker arm merely pivots, but the engine poppet valve does not move and therefore, is in its deactivated condition.
Although the known valve deactivator sub-assemblies of the type referred to above have performed in a generally satisfactory manner, such sub-assemblies do add substantially to the overall cost of the valve gear train, and in many cases also add undesirably to the space taken up by the overall rocker arm installation. In some engine designs, there is simply no room to add a valve deactivator sub-assembly of the type which is associated with the rocker arm fulcrum member.
Typically, in a push rod type of valve gear train, there is some sort of cam follower device having one portion thereof in engagement with the cam lobe on the engine cam shaft, and another portion thereof in engagement with the lower end of the push rod. It is also known for such a cam follower mechanism to include a hydraulic lash compensation element. It is now also known to incorporate a valve deactivator mechanism into the cam follower, thus eliminating the need for adding to the rocker arm assembly the type of expensive, space consuming deactivator structure described above, for use with a rocker arm fulcrum member.
On a normal internal combustion engine having valve gear train of the push rod type, as described above, and including some form of valve deactivation capability, it would be typical for less than all of the engine poppet valves to be equipped with the valve deactivation capability. In other words, on an eight cylinder engine, by way of example only, it would be typical to provide valve deactivation capability on both the intake and exhaust valves of four of the eight cylinders, while equipping the intake and exhaust valves of the other four cylinders with conventional roller followers.
The valve deactivating cam followers of the type to which the present invention relates typically include some sort of latching mechanism, operable to latch the follower, so that rotation of the camshaft results in cyclical up and down motion of the follower (and of the push rod). The latching mechanism is also operable to be in an unlatched condition of the cam follower, thus introducing lost motion into the valve gear train, so that rotation of the camshaft results in no up and down motion of the cam follower (and no up and down motion of the push rod). Typically, although the present invention is not so limited, the latching mechanism includes a radially moveable latch member, perhaps biased radially outwardly by a biasing spring, toward the latched condition. In that case, unlatching is accomplished by communicating pressurized control fluid through a control passage in the engine block to the bore in which the cam follower reciprocates, where the control pressure biases the latch member radially inward, in opposition to the biasing force of the spring, to the unlatched condition. A valve deactivating roller follower of the type described above is known from U.S. Pat. No. 6,196,175, assigned to the assignee of the present invention and incorporated herein by reference.
Although valve deactivating cam followers of the type described above are starting to achieve commercial use, and are performing well, the environment in which such cam followers operate inherently results in certain problems. In connection with the development of the present invention, it has been observed that, occasionally, the response time of the cam follower (i.e., the time to change between the latched and unlatched conditions) is much slower than anticipated, and much slower than is required for optimum engine operation. It has also been observed that the sudden, substantial increase in the response time of the cam followers is generally accompanied by the presence of air in the pressurized fluid in the control passage. Typically, the xe2x80x9clowerxe2x80x9d end of the cam follower, i.e., the end where the roller is mounted, is disposed adjacent an opening in the engine block, with the camshaft being disposed in this opening, and engaging the roller of the cam follower.
Accordingly, it is an object of the present invention to provide an improved valve deactivation assembly which overcomes the above-described disadvantages of the prior art.
It is a more specific object of the present invention to provide an improved valve deactivation assembly, especially suited for use in push rod type valve gear train, wherein the deactivation assembly does not encounter such occasional, substantial increases in response time.
It is another object of the present invention to provide an improved valve deactivation assembly which accomplishes the above-stated objects by minimizing the ability of air to pass from the opening surrounding the camshaft to the control fluid passage containing the pressurized fluid used to control the latching mechanism.
The above and other objects of the invention are accomplished by the provision of an improved valve deactivation assembly for an internal combustion engine of the type having valve means for controlling flow to and from a combustion chamber. A drive means provides cyclical motion for opening and closing the valve means in timed relationship to the events in the combustion chamber. A valve gear train is operative in response to the cyclical motion to effect cyclical opening and closing of the valve means. The valve deactivation assembly comprises part of the valve gear train and is disposed in a bore defined by the internal combustion engine, and includes latching means shiftable between latched and unlatched conditions in response to the presence of a control fluid pressure in a control passage intersecting the bore. The valve deactivation assembly includes an outer body member disposed for reciprocable movement in the bore in response to the cyclical motion of the drive means.
The improved valve deactivation assembly is characterized by the bore defining a lower terminal portion disposed adjacent the drive means. The other body member defines on its outer surface a fluid chamber extending about substantially the entire circumferential extent of the outer surface, the fluid chamber remaining aligned with the bore, between the lower terminal portion of the bore and the control passage as the outer body member engages in the reciprocable movement. One of the outer body member and the bore defines a fluid passage disposed to communicate between a source of fluid pressure and the fluid chamber to form a barrier to substantially block (or xe2x80x9csealxe2x80x9d) the migration of air from the lower terminal portion of the bore to the control passage in association with reciprocable movement of the outer body member.